Field of the Invention
The present invention relates generally to ophthalmic lenses and laser vision correction, and more particularly, to a method for designing, evaluating and optimizing ophthalmic lenses and laser vision correction in order to optimally manage issues resulting from, or related with, halos.
Description of the Background
Ophthalmic lenses, such as intraocular lenses (IOLs), phakic IOLs, piggyback IOLs, spectacle lenses, contact lenses, and corneal implants may be used to enhance or correct vision. For example, IOLs are routinely used to replace the crystalline lens of an eye during cataract surgery.
Ophthalmic lenses, such as IOLs may be monofocal or multifocal. A monofocal IOL provides a single focal point, whereas a multifocal IOL provides multiple focal points for correcting vision at different distances. For example, a bifocal IOL provides two different focal points, routinely one for near vision and one for distant vision.
Ophthalmic lenses, such as the aforementioned multifocal IOLs, may be refractive, diffractive, or both refractive and diffractive. Multifocal refractive IOLs may be comprised of several concentric annular optical zones with each zone providing for a near or a far focus. A diffractive multifocal IOL is generally divided into a plurality of annular zones, or echelettes, that are offset parallel to the optical axis by predetermined diffractive step heights in order to provide a specific phase relationship between the annular zones. A diffractive multifocal IOL may divide incident light into two diffractive orders to provide near and distant vision.
Although multifocal lenses are effective for vision correction, further enhancements would be advantageous. One problem associated with multifocal/bifocal IOLs, in part due to the typically bifocal configuration of the refractive/diffractive zones, is dysphotopsia, and in particular halos under low light conditions. Halos may arise when light from the unused focal image creates an out-of-focus image that is superimposed on the used focal image. For example, if light from a distant point source is imaged onto the retina by the distant focus of a bifocal IOL, the near focus of the IOL will simultaneously superimpose a defocused image on top of the image formed by the distant focus. This defocused image may manifest itself in the form of a ring of light surrounding the in-focus image, and is referred to as a halo. In addition to multifocality, add power and light distribution may also contribute to dysphotopsia.
Discomfort, visual disturbance or nuisance from dysphotopsia may be tied to personal attributes or habits. For example, a patient's psychological profile may play an important role; more critical patients may be more affected by halos than those less critical. In addition, habitual circumstances may influence discomfort, e.g. truck drivers are typically more affected by halos due to night driving.
Aberrations of the cornea and in particular higher order corneal aberrations have a direct impact on halos. Corneal topographic analysis using photokeratoscopic or videokeratographic methods provides objective measures of corneal topography. Current measurement devices typically employ several concentric rings or multiple discrete light sources to reflect a luminous object of known dimension from the cornea. The size of the cornea-reflected images of this object is then measured with photographic or electro-optical recording methods to compare the shape of the cornea with a theoretical spherical shape. If the cornea is spherical, for example, the reflected images of the ring-shaped objects will be equally spaced, continuous, concentric ring-shaped patterns. If the cornea has surface defects, or is not precisely spherical, the resultant ring images will be less equally spaced or will have a different shape, such as an elliptical shape.
Corneal topography can thus be used to determine the optical aberrations of the cornea. Such aberrations in conjunction with the designs, methods, and systems disclosed herein may be used to manage halos. And, based on the aforementioned, a need exists for a lens design and, more particularly, to an apparatus, system and method for designing, evaluating and optimizing ophthalmic lenses for such management.